Base the plausibility check on the totalized mass flow computed within the coriolis meter.  Chose some time interval - one minute, five minutes, or whatever you prefer.  The total mass through the coriolis meter is the change in the totalized mass flow over this interval (the longer the time interval, the less the difference is affected by the pulsing frequency). Compare this to the total mass flow computed from the pump stroke data.  You could also compute a "meter factor" to force the flow computed from the pump stroke data to agree with the coriolis meter.

Base the instantaneous ratio on the mass flow computed from the pump stroke data.  But if you have a batch process and the ratio of the total amount fed is most important, you could use the totalized mass flow from the coriolis meter.